It seems safe to say that most of us want to keep our secrets to ourselves. It might even be a fundamental part of the human experience to want control over who knows what about you - and to ensure that it stays that way. And yet with the constant emergence of new technology, this concept now starts to apply to how confidential information is transferred between units, not just between whispering people. But fortunately, there is a whole field of technology that holds the secret of how to keep our information safe: cryptography.

Cryptography is the deceptively simple practice of making data illegible so that it is secure enough to send over to its recipient. This is done with a key which works very similarly to physical keys; they make data accessible (decrypt) or inaccessible (encrypt). Cryptography is essential for the security of our data, but does the encryption of data necessarily mean that it’s private - and are these encryption algorithms truly unbreakable?

For us to understand this question, we’ll have to know some of the history.

Let's think back to the Roman Empire; believe it or not cryptography was relevant during this time, so much so that Julius Caesar would utilise the early practice in order to transmit secret messages and in turn created his own encryption method. To envision this let's put ourselves in Caesar's shoes. When you're on the brink of assassination by those closest to you, you're going to need a bit of privacy. His method was known as the Caesar Cipher, one of the earliest records of encryption. How it would work is that each letter in a sentence would be shifted by three spaces in the alphabet to create a cipher text or encrypted text. Straightforward? Sure. Secure? Not so much. What characterises good encryption methods is their keys having a degree of randomness to them to decrease the chances of anything predictable, to be long in length with most having a minimum of 128 bits (2128 different combinations), and to have a relatively complex algorithm. So although the Caesar Cipher may provide temporary confidentiality if the system is not entirely understood, it is unable to match the demands of today's encryption standards and is incredibly of its time.

Fast forward to the 20th century, in the unwavering rage of WW2 cryptography was heavily relied upon to send messages integral to the continuation of the war. A fundamental example of this was the Enigma machine, used by the Germans and famously conquered by British mathematician Alan Turing…

With resemblance to a typewriter, when a key was pressed on the keyboard of the Enigma this would send a signal through wires to the rotors which would then assign the letter pressed with a new letter. Depending on the number of rotors the machine had, the original letter would change multiple times passing through each router, one time through one rotor, a second time through the next and so on. To maintain security of the system the rotors could be configured differently to give a different combination of letters each time and these key settings were changed daily. This may seem impressively robust; however, Alan Turing and his colleagues were able to find a flaw that allowed them to crack the code. With this flaw the codebreakers were able to shorten the war by a considerable amount of time; all by having an understanding of the Enigma machines weaknesses. And so from ancient Rome to World War II, from easy to break ciphers to enigma codes and more we can see how cryptography has grown and developed from its foundational ideas to being a key component for internet confidentiality.

With your new learnt knowledge you may be under the impression that modern day cryptography methods all must have some sort of limitation but to what extent is this true? Two modern day encryption techniques are RSA and AES; both given the title of unbreakable. AES is a symmetric encryption technique which means it uses a singular private key which must be securely sent between the two parties to both encrypt and decrypt data as opposed to RSA which is an asymmetric technique; a public key for encryption and a private key for decryption. AES and RSA can work hand in hand to effectively encrypt and decrypt data, let's picture it: you’d like to send your friend a cake for their birthday but it's incredibly important that nobody else - thieves lets say - can have a taste. So what do you do? You send your friend the cake in a tightly sealed container (AES encryption) however your friend won't know how to open this container unless you give them the same instructions (public key) you used to close it. As a solution you use a special delivery service (RSA encryption) which ensures that no one else has access to your instructions. Now when your friend receives the container, they can safely open it (AES decryption) to access their cake. This paired with the common standard of 256 bit keys (2^256 combinations of different keys) means AES is virtually impossible to break as attempting to do so with a brute force method i.e attempting every combination of key to decrypt the ciphertext would be a computational infeasibility meaning it would take billions of years to do so even using a high-end GPU made for completing multiple calculations at once. So to answer the question on whether or not modern day cryptography methods have their limits, probably not for now!

Nonetheless, there is a major threat to modern day cryptography, with that being quantum computers. Although largely theoretical for now, quantum computers could have the potential to push our modern day systems into a ‘quantum cryptography’ era taking our billions of years of processing to perhaps a lifetime or less. An example of this is quantum key distribution (QKD) which uses the principles of quantum mechanics such as superposition (rather than bits being either a zero or one they can be both simultaneously) and the observer effect (the observation of a quantum system having an effect on the system itself to detect eavesdropping).

As technological innovations expand beyond limits we had previously deemed impossible, the field of cryptography continues to evolve alongside it. From Julius Caesar to quantum methodologies one thing has remained the same: the enduring human need to control who knows what about us and to keep our secrets safe.